1. Technical Field
The invention relates to electronic circuit boards and more particularly to multi-layer circuit boards exhibiting high thermal conductivity for heat dissipation and providing for double sided mounting of circuit elements to achieve high circuit element volumetric density.
2. Description of the Related Art
Contemporary electronic circuits are conventionally fabricated by mounting circuit elements and integrated circuit packages on circuit cards or boards. The boards electrically interconnect the various passive and active circuit elements and integrated circuit packages into one or more functional units. Conventional multi-layer boards are manufactured by laminating together layers of, for example, glass reinforced epoxy, and have copper conductors affixed to one or more major surfaces of the board. Circuit elements may then be attached to the conductors to complete the device.
While laminate boards composed of non-thermally conductive materials are suitable for many low density applications, such boards are less than optimum for application to power supplies and other applications having a high density of circuit elements. Power supplies are often rated on the basis of watts per unit volume. Components such as transformers and filters can be reduced in size if operating frequency is increased. Higher operating frequencies though place a premium on short, low inductance connections between circuit elements. It is also preferable if use of both sides of a circuit board for support of devices is allowed. In this way the smaller devices are brought physically closer together. However, reduced size reduces the surface area of the device from which to radiate heat. Close physical proximity to other heat generating devices complicates the heat dissipation process. As a consequence, heat removal, which is already a problem for boards used for power supplies, promises to become still more difficult as operating frequencies are increased from the 50 to 200 kilohertz range to ranges in excess of 1 Megahertz.
The use of insulated metal core circuit boards to increase heat dissipation is known. Although high thermal conductivity to the metal core is also known, it has been limited to use on single sided boards.